Applications for gas sensors have gained significant interest in the past few years due to growing concerns over air pollution and global climate change. For example, carbon dioxide sensors are commonly used to measure machine emissions and indoor air quality. There are a number of general methods of measuring a gas concentration. A chemical sensor measures a gas concentration by measuring an electrical property of a gas sensitive material, such as a metal oxide (MOX) or graphene. On the other hand, a physical sensor measures a gas concentration by exposing a gas sample to an infrared light source and performing a physical measurement on the gas. For example, a non-dispersive infrared absorbance (NDIR) sensor measures the absorption of the infrared light a certain wavelengths and determines the gas concentration based on the amount of light absorption; and a photoacoustic sensor measures a change in pressure of the gas sample in the presence of infrared light and determines the gas concentration based on the change in pressure of the gas.
Photoacoustic sensors, which generally include an infrared light source and a microphone, are well-suited to low-cost and mass producible implementations because of their small size and their ability to be manufactured using common commercial semiconductor and packaging technologies. One issue with photoacoustic sensors, however, is their sensitivity to acoustic noise. Acoustic noise produced by machinery, traffic, or even human activity may interfere with the photoacoustic sensor's ability to perform acoustic measurements and degrade the accuracy of the sensor.